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Different disinfecting solutions used during storage in cases result in different levels of contamination and contamination by different types of microbes. These differences are not simply because of the types of disinfectants used, suggesting that other excipients in, or formulation of, the solution affect contact lens storage case contamination.

Frequent replacement of lens cases may reduce microbial contamination. Future studies should specify the areas swabbed in the lens case. Better lens storage case design and additional hygiene attention need to be introduced to reduce contamination in these "risky" areas.

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The external ocular surface of children is contaminated with gram-positive bacteria that are resident microbiota. During lens wear, there was a trend for lesser recovery of organisms from the upper bulbar conjunctival samples,but there was no change in the type of microorganisms isolated. At all times, lower lid margins showed consistently greater colonization and is a source of potential contamination of the conjunctival surface.

Enhanced survival of Acanthamoeba castellanii has previously been reported following co-incubation with a single strain of Pseudomonas aeruginosa. The aim of this study was to evaluate the impact of different strains of P. aeruginosa on amoebae survival. Four contact lens solutions were challenged with A. castellanii for between 6 and 24 h, and survival rates of amoeba were calculated. Subsequently, A. castellanii was co-incubated with different strains of P. aeruginosa (strain 6294, an invasive isolate; 6206, a cytotoxic isolate; and Paer 001, a null isolate). Differences in amoeba survival over time between solutions for each bacterial strain were analysed. Non-neutralized hydrogen peroxide was the most effective system against A. castellani at all time points (P<0.05). Survival rates were not different between multipurpose solutions and neutralized hydrogen peroxide. Co-incubation with P. aeruginosa altered amoeba survival, and maximum survival occurred in the presence of the invasive strain of P. aeruginosa. Enhanced amoeba survival may occur in the presence of certain strains of Gram-negative bacteria, and with certain types of contact lens disinfection systems.

The alternative guidelines are more effective in eliminating microbial contamination from lens cases than that of the current manufacturer's guideline. Simply incorporating rubbing and tissue-wiping steps in daily case hygiene reduces viable organism contamination.